Wordpress plugin interacting with custom table

This is my first foray into the world of Wordpress plugins.

I have managed to create the plugin, activate it and display records from a custom table.

Now I want to be able to add/edit/delete records from href tags using AJAX

This is my code thus far, however, it is not deleting the selected record.

<?php
    global $wpdb;
    $items = $wpdb->get_results("SELECT * FROM wp_freight;");
    echo "<h1>Plate Costs</h1>";
    echo "<table class='wp-list-table widefat fixed users'>";
    echo "<tr><thead><th>ID</th><th>Origin</th><th>Destination</th>   <th>Price</th><th></th></tr><thead>";
    foreach($items as $item){
       echo "<tbody><tr>";
       echo "<td>".$item->id."</td>";
       echo "<td>".$item->origin."</td>";
       echo "<td>".$item->destination."</td>";
       echo "<td>".$item->price."</td>";
       echo "<td><a class='button button-primary' href='' style='margin-   right:10px'>Edit</a><a class='button button-primary' href='#'   onclick='ajaxDeleteItem(".$item->id.")'>Delete</a></td>";
       echo "</tr></tbody>";
     }
     echo "</table>";   


    function delete_row() {
        $id = $_POST['element_id'];
        $table = 'wp_freight';
        $wpdb->delete( $table, array( 'id' => $id ) );
        echo $id;
    }

    add_action('wp_ajax_your_delete_action', 'delete_row');
    add_action( 'wp_ajax_nopriv_your_delete_action', 'delete_row'); 

?>

<script>
    function ajaxDeleteItem(a){
    var dataString = 'userID='+ a;
    jQuery.ajax({
        type: "POST",
        url: ajaxurl,
        data: {"action": "your_delete_action", "element_id": a},
        success: function(msg){
            alert( "Item " + a + " deleted." );
        },
        error: function(){
            alert('failure');
          }
    });
    }
</script>